1. Field of the Invention
The present invention relates to a polymer thin film having a microphase-separated structure in which cylindrical phases (a cylindrical microdomain) distributed in a continuous phase are oriented in a pass-through direction of the polymer thin film and provided in a substantially periodic array pattern, and a method of manufacturing the same. The present invention also relates to a patterned substrate having on its surface the periodic array pattern of the microphase-separated structure, and a method of manufacturing the same. The present invention also relates to a patterned medium for magnetic recording manufactured by using the patterned substrate, and a method of manufacturing the same.
2. Description of the Related Art
An electronic device, an energy storage device, and a sensor, or the like have been increasingly reduced in size and have achieved higher performance these years. This requires that a minute periodic array pattern in several nanometers to several hundred nanometers scales be created on a substrate. There is a need for establishing a process of manufacturing a minute pattern with high precision and at low cost. A top-down technique such as lithography is generally used for creating such a minute pattern by minutely cutting a bulk material. For example, photo lithography is typically used in processing a semiconductor such as a LSI.
As a pattern becomes minuter, the top-down technique has more difficulty in terms of an equipment and a process for manufacturing a minute pattern. In particular, if a minute pattern is processed in a several tens nanometers scale or less, the pattern has to be processed using an electron beam or deep ultraviolet rays, which requires an equipment with a large amount of investment. Further, if a pattern is too minute to make it impossible to be created using a mask, a direct writing technique has to be used, which significantly reduces a process throughput.
Under such circumstances, a process applying a self-assembly phenomenon, in which a material organizes a structure by itself, receives much attention. In particular, a process applying the self-assembly phenomenon, a so-called microphase separation, of a block copolymer is excellent in being capable of creating a minute periodic structure having various shapes in tens to hundreds of nanometers scales.
If different polymer block chains constituting a block copolymer are not mixed with each other (incompatible), a specific minute structure having a periodic array pattern is self-assembled thanks to a microphase separation of the polymer block chains.
Techniques of creating a minute periodic pattern using the self-assembly phenomenon have been known, in which, for example, a substrate is etched using a block copolymer composed of a combination such as polystyrene and polybutadiene, polystyrene and polyisoprene, polystyrene and polymethylmethacrylate, as a mask, to thereby create a structure such as a hole, a line and space pattern, or the like (see, for example, “Block Copolymer Lithography Periodic Arrays of ˜1011 Holes in 1 Square Centimeter”, M. Park, C. Harrison, P. M. Chaikin, R. A. Register, D. H. Adamson, Science, Vol. 276 (1997) pp. 1401-1404, and “Enabling nanotechnology with self assembled block copolymer patterns”, C. Park, J. Yoon, E. L. Thomas, Polymer, Vol. 44 (2003) pp. 6725-6760).
The microphase separation phenomenon of block copolymers enables to obtain a polymer thin film having a structure in which a spherical or cylindrical microdomain is periodically arrayed in a continuous phase.
If the obtained microphase-separated structure is used as a patterned substrate such as an etching mask, it is desirable that cylindrical phases are provided in a period array pattern and are oriented perpendicular to a substrate (in a pass-through direction of the polymer thin film) in a continuous phase.
This is because the structure in which the cylindrical phases are oriented perpendicular to the substrate has a flexibility in changing its aspect ratio, compared to a structure in which a spherical microdomain are provided in a periodic array pattern on a surface of a substrate. The aspect ratio of a domain is a ratio of a size of a domain in perpendicular direction to a substrate, to a size of a domain in parallel to the substrate.
If the microphase-separated structure having the spherical microdomain is used as a patterned substrate for use in an etching mask or the like, its maximum aspect ratio is 1, which is smaller than that of the structure having the cylindrical phases. That is, the structure with the spherical microdomain has smaller control flexibility than that with the cylindrical phases.
Nevertheless, the structure with the cylindrical phases composed of the block copolymers caused by the microphase separation are often oriented parallel to the substrate.
Conventional techniques for orienting the cylindrical phases perpendicular to a substrate (in the pass-through direction of the polymer thin film) are as follows.
A first conventional technique to obtain a microstructure oriented perpendicular to a substrate is that an extremely high electric field is applied to a film composed of block copolymers in a pass-through direction thereof, to thereby orient cylindrical phases thereof in a direction of the electric field (see, for example, “Effect of an Electric Field on Block Copolymer Microstructure”, K. Amundson, E. Helfand, D. D. Davis, X. Quan, S. S. Patel, S. D. Smith, Macromolecules, Vol. 24 (1991), pp. 6546-6548).
A second technique is that a surface of a substrate is chemically modified, and is treated to have an equal affinity for each block chain of block copolymers. (see, for example, “Neutrality Conditions for Block Copolymer Systems on Random Copolymer Brush Surfaces”, E. Huang, S. Pruzinsky, T. P. Russell, Macromolecules, Vol. 32 (1999), pp. 5299-5303).
A third technique is that a thin film made of a block copolymer composed of three different block chains is formed while inducing a gradual change in a thickness of the film. It has been reported that a microstructure having cylindrical phases oriented perpendicular to a surface of the film are sometimes be created in a region in the film having a specific thicknesses (see, for example, “Phase Behavior in Thin Films of Cylinder-Forming Block Copolymers”, A. Knoll, A. Horvat, K. S. Lyakhova, G. Krausch, G. J. A. Sevink, A. V. Zvelindovsky, and R. Magerle, Physical Review Letters, Vol. 89 (2002), No. 3, pp. 035501-1 to 035501-4).
A fourth technique is that, in a technological field of a separation film (a permselective film), a block copolymer composed of polymer chains, which are incompatible with each other, is microphase-separated, and resultant cylindrical phases are selectively removed to obtain a porous film having micropores (see, for example, Japanese Laid-Open Patent Application, Publication No. HEI 5-287084, paragraph 32).
However, the first conventional technique has a problem that, in order to apply the extremely high electric field to the film composed of block copolymers, voltage has to be applied to an extremely narrow gap between a surface of the film and an electrode which are closely contacted with each other.
The second conventional technique has a problem that it is not generally easy to treat the surface of the substrate such that the surface has an equal affinity for each block chain of the block copolymers.
The third conventional technique has a problem that the film is required to have a gradual change in its thickness, which makes it impossible to obtain a substrate having a structure in which the cylindrical phases are uniformly provided over and perpendicular to the substrate.
The conventional techniques above are thus not suitable for providing a structure in which the cylindrical phases are oriented perpendicular to a substrate.
That is, those techniques making use of a microphase separation of block copolymers are still convenient and low in cost to obtain a minute periodic structure in a several tens to several hundreds of nanometers scale. However, the techniques have a difficulty in obtaining the structure having the cylindrical phases perpendicular to a substrate.
The fourth conventional technique has a problem that a periodic array pattern of the cylindrical phases distributed in the continuous phase can be obtained only in a limited portion of the polymer thin film.
The present invention has been made in an attempt to solve the problems described above, and provides a polymer thin film in which the cylindrical phases are extensively provided in a periodic array pattern and in the pass-through direction of the polymer thin film, making use of a microphase separation of the block copolymers. The present invention also provides a method of manufacturing a patterned substrate having on its surface the periodic array pattern of the microphase-separated structure. The present invention also provides a method of mass-producing a patterned medium for magnetic recording capable of, for example, increasing a recording density, by transferring a pattern of the patterned substrate onto the patterned medium.